The present invention relates to a quiet valve, and more particularly to a novel and improved labyrinth trim to achieve an orderly and silent dissipation of fluid energy in a throttling process.
In a typical system utilizing fluid flowing at high velocity and under high pressure, it is often necessary to reduce the pressure and velocity of the fluid. Accordingly, many prior art devices have been proposed wherein a fluid flow restrictor means is arranged intermediate the inlet and outlet of a valve structure to effect a controlled, multiple stage dissipation of the fluid energy. In such a valve, the potential energy of the fluid is converted into kinetic energy by throttling the flow. The kinetic energy is then dissipated by a controlled turbulence. A problem associated with high pressure drop valves is the acoustic energy generated by the turbulence. The objectionable noise is caused primarily by sudden drops in pressure as the fluid flows through the valve. Therefore, the fluid is typically caused to flow through labyrinthine paths resulting in a gradual dissipation of energy either through multiple changes of direction, controlled and limited expansion, friction or a combination of these. The result is a pressure drop at any one stage of the fluid flow restrictor which is sufficiently low to avoid the generation of excessive noise and/or cavitation.
In many prior art devices of the above-described type, the fluid flow restrictor comprises a series of axially aligned and stacked discs. The discs are provided with various arrangements of fluid flow paths to effect the energy dissipation. The flow paths are uncovered by the axial motion of a close-fitting valve plug received in a cylindrical opening formed through the center of the stacked discs. In other devices, the axial movement of a valve plug uncovers small openings in a cylindrical sleeve. A problem with each of these types of devices is that the openings and fluid flow paths are prone to plugging or jamming by particulate matter in the flow stream. In still other devices, a tapered plug fits a tapered seat and the axial movement of the plug exposes a series of orifice lands and grooves formed on one or both of the mating parts. These devices are effective for only a small amount of plug lift, which is undesirable in applications requiring large flows with high pressure drops.
It is a primary objective of the present invention to provide a fluid flow control valve which is economical to manufacture, highly effective in controllably dissipating fluid energy, and which obviates the disadvantages of the above-discussed prior art devices. Generally, the valve disclosed herein comprises a plurality of closely interfitting concentric cylinders alternately fastened to the valve seat and valve plug. The valve plug is arranged for axial movement relative to the valve seat whereby the interfitting cylinders may be axially displaced with respect to one another. A plurality of slot-like openings are formed in each of the cylinders to act as limited expansion chambers for the fluid. The slots are arranged throughout the several concentric cylinders in various geometric patterns to provide restricting orifices or laminar flow paths for fluid communication between the openings of adjacent cylinders. In this manner, the fluid is permitted to flow through a series of expansion stages to gradually dissipate the kinetic energy and reduce fluid pressure without the generation of excessive noise and/or cavitation.
In accordance with one advantageous form of the invention, the openings are in the form of axially elongated rectangular slots. The slots of each cylinder overlap the slots of the adjacent, interfitting cylinder whereby the sharp corners on the sides of the slots define a restricting orifice between the openings. The orifice width is determined by the angular orientation between the interfitting cylinders and the orifice length is determined by the axial movement of the cylinders fastened to the valve plug. The cylinders may be constrained against rotation such that the orifice width is constant and the orifice length is a function of the axial movement of the valve plug providing an orifice area which varies linearly with plug travel.
To advantage, the cylinders may be oriented such that the right side edge of each opening always overlaps the left side edge of the adjacent opening whereby the fluid will flow in spiral paths with respect to the axis of the cylinders. In another advantageous form, the cylinders may be aligned whereby the right side edge of one opening overlaps the left side edge of the adjacent opening and the left side edge of the adjacent opening overlaps the right side edge of the next adjacent opening and so on. The fluid will flow along paths which are in a generaly zig-zag pattern about radial lines of the cylinders.
In accordance with another specific form of the invention, the slots of each cylinder may be centered between the slots of adjacent cylinders and the mating relationship between the cylinders is such that a narrow spacing exists to define long flow paths of laminar dimensions between openings. As the fluid flows out of each slot it will be divided into two paths and flow circumferentially between the cylinders to the two adjacent slots of the adjacent cylinders. The velocity of the flowing fluid effectively limited by viscous friction at the cylinder walls. This embodiment is especially well suited for flow control with a fixed pressure differential.
In still another form of viscous friction control taught by the present invention, the concentric cylinders are unslotted and the fluid flow is axial between a first pair of mating cylinders into the open volume at the end of one of the cylinders and then into the clearance between the next adjacent pair of cylinders. This arrangement is particularly suited to pressure control applications.
Of course, the valve of the present invention may include other features. For example, the shape of the slot openings may be trapezoidal or triangular in shape to vary the width of the orifice in relation to axial movement of the valve plug. The cylinders attached to the valve plug also may be keyed for predetermined rotational movement as the valve plug is raised.
For a better understanding of these and other features and advantages of the present invention, reference should be made to the following detailed description of preferred embodiments and to the accompanying drawings.